A battery separator is used to separate the positive and negative electrodes of a battery, for example, a secondary lithium battery. A battery separator is typically microporous to allow ionic current with least possible resistance.
In general, a battery separator is sandwiched between the positive electrode and the negative electrode of a secondary lithium battery. It is important for a battery separator to remain in its proper position because even a minute displacement may cause a short in the battery. Currently there are no prevailing techniques to determine the position of a separator in a battery to prevent the introduction of flawed batteries, i.e. those batteries in which the battery separator was displaced during the manufacturing process, into the consumer market.
U.S. Pat. No. 3,861,963 discloses a porous separator, which is coated or impregnated with an inorganic material. The inorganic coating may be an insoluble metal oxide and insoluble hydrous metal oxides such as the oxides and hydrous oxides of Zr, Ti, Sb, W, Si, Sc, Bi, V, Al, and Ce. The coating, however, constitutes about 15-32 percent by weight of the separator.
U.S. Pat. No. 5,154,988 discloses a battery separator comprising of three layers, which include a base web, a glass mat, and a natural rubber. The base web includes a filler such as silica and small amounts of alum and other retention aids such as cationic or anionic copolymers, including cationically or anionically modified high molecular weight polyacrylamide.
U.S. Pat. No. 5,336,573 discloses a separator comprising a microporous membrane sheet composed of substantially uniform mixture of a polymer and a filler present in a weight ratio of about 1:2.5 to about 1:30 which has a fibrous sheet encapsulated therein.
U.S. Pat. No. 5,654,115 discloses a hydrogen-absorbing alloy for a battery capable of satisfying leading characteristics of high electrode capacity, and long life. An X-ray microanalyzer is employed to determine the weight percent of the hydrogen-absorbing particles.
U.S. Pat. No. 6,348,286 discloses an alkaline battery separator comprising a fiber sheet containing, on the outer surface of fiber sheet, a substance having a peak of bond energy at 503.5 to 5.31.5 eV. The peak of the bond energy is measured via an X-ray photoelectron spectrometer.
U.S. Pat. No. 6,420,070 discloses an electrode made of a graphite material capable of intercalating and de-intercalating lithium ions. CuK α as the X-ray source is utilized to determine the wide angle X-ray diffraction of the electrode.
U.S. Pat. No. 6,423,445 discloses a battery separator comprising a gas-permeable sheet that contains a hydrophilic portion carrying a methacrylic/ethylene copolymer component having a crystalinity of 25% or more on at least a part of surface of the hydrophobic portion. Fluorescent X-ray method is utilized to measure X-ray intensity thereby determining the amount of sulfur atoms per unit of area.
U.S. Pat. No. 6,432,586 discloses a separator for a high-energy rechargeable lithium battery. The separator comprises a ceramic composite layer and a polymeric microporous layer. The ceramic composite layer comprises a matrix material having inorganic particles dispersed therethrough. The inorganic particles may be selected from SiO2, Al2O3, CaCO3, TiO2, SiS2, SiPO4, and the like, or mixtures thereof. The inorganic particles form approximately 20-95% by weight of the ceramic composite layer.
U.S. Pat. No. 6,713,217 discloses a hybrid separator.
Despite the research efforts in developing battery separators, there is a still a need for a battery separator, which is readily detectable when embedded in a battery to determine its position within the battery, and it is relatively easy to manufacture at a low cost. Furthermore, there is still a need for a method for detecting the position of a separator in a battery, which is relatively easy and cost effective.